In recent years there has been an increasing requirement for extremely pure gases. This as been particularly true in the semi-conductor industry which uses both active and inert gases. Commonly, gases are supplied to such industries in the form of liquified gases which are then vaporized just prior to use. Various contaminants have been found in very small amounts in such liquified gases. Some of these impurities are originally present in the gas during manufacture and others are generated during the storage of the gases as a result of a contamination from storage vessels, condensation of moisture, exposure to air and other materials during the manufacture, transport, or storage thereof.
The requirements for such pure gases in the semi-conductor industry limit specific impurities to less than one part per million. For example, less than 1 ppm of water or carbon dioxide can be tolerated. These contaminants, both water and carbon dioxide, are commonly found in liquified gases in both solid and dissolved forms. Water can be initially present during the manufacture or can be picked up during the transport and storage of the liquified gases. Another common contaminant which can create problems is the presence of carbon dioxide in liquified oxygen.
While it has been known in the prior art to remove impurities from liquified gases using adsorbents, a method for the removal of such contaminants to the extent of producing a gas having less than 1 ppm of contaminants which is capable of being employed on site has not been available. Thus, the invention disclosed herein seeks to provide purification of liquified gases at various stages including: prior to storage, subsequent to storage, and prior to use.
The purificiation method and apparatus of the invention can also be used within storage tanks and within delivery trucks. In fact, the invention provides purification at any stage of transport of such liquified gases so that the resulting gases are highly purified and do not cause malfuntioning of instruments due to contaminants or the subsequent contamination of products, especially in the semi-conductor industry.